Technical Tidbit - Collimated Sputtering

One of the biggest problems with sputter deposition is filling contacts and vias. The larger the step height or aspect ratio is, the bigger the challenge to properly fill the contact or via. Some undesirable effects include thinning, cracking, and overhangs. The overhang is sometimes referred to as breadloafing, named for the shape that bread makes when it expands past the top of its baking pan. While heating wafers improves step coverage, it does not solve the problem. The material entering a recessed feature (e.g., via or contact) must be spread over all surfaces of the feature (5 sides); this decreases the deposited film thickness per unit area. It is progressively more difficult to fill holes as aspect ratio increases. The film deposition rate is higher at top corners of holes because atoms arrive here from a larger range of angles. This produces an overhang that can cause several serious problems. The deposition rate on sidewalls decreases with time, and shadowing limits deposition on the bottom corners of hole. Eventually the hole closes completely, causing a void.

One solution is collimated sputtering. A metal honeycomb collimator is inserted between target and wafer. It traps oblique-angle vapor atoms, reducing the number of atoms hitting the surface at oblique angles. The aspect ratio of collimator is normally adjustable. This technique has several negative consequences. First, it significantly reduces deposition rate, making for longer deposition times. Second, the deposition rate decreases with time as collimator become coated. And third, the collimator must be replaced frequently.

Another solution is long throw collimated sputtering. In this approach, no physical collimator used. Instead the target-wafer separation increased from ~ 5 cm to ~ 30 cm. The oblique-angled vapor atoms never reach the wafer, striking the chamber walls instead. The pressure lowered to ~0.1 mtorr to increase the mean-free path of the atoms. The disadvantage of this technique is that the cross-wafer uniformity of hole filling is not ideal.

A third solution that is used for used for processes below the 0.25µm node where aspect ratios > 3:1 is ionized sputtering. In this technique, the sputtered atoms are ionized in flight. A bias on wafer controls energy & direction of these ions. There are several advantages, including excellent hole filling, no overhang, longer target life, and less frequent chamber cleaning. The disadvantages to this technique are more complex equipment, and a more expensive process.

Online Training

Semitracks' new and improved Online Training is convenient, up-to-date, and cost effective. Access the same material presented in our courses whenever you need it, right when you need it without having to worry about the high costs and hassle of traveling. The semiconductor field is an ever-changing one. With access to the most current information, you can stay on top of the new technology. Online Training is also very cost effective. For only $500 per year, you gain access to thousands of dollars worth of courses and course material.

Give our Online Training a try – for free. This month's topic is Lead Free Issues in Semiconductor Packaging.

This segment is no longer available. If this topic interests you, perhaps you would be interested in our Online Training. For more information or to sign up, please visit http://www.semitracks.com/online-training/.

Course Spotlight - Design Debug

Designing complex integrated circuits is a daunting task. Designers must not only manage the design complexity and verification process, but also locate the sources of subtle defects and design/manufacturing interactions. The ability to quickly resolve design problems can make or break a product design. It can even make or break your company. The designers, test engineers, and failure analysts must team together to quickly resolve these issues. This requires specialized knowledge in design debug tools and techniques.

This course covers post-silicon debug and the role of physical probing tools (especially optical probing equipment) in debug. The expected audience is anyone involved with post-silicon debug who wants to learn: what are the capabilities of probers; how best to utilize optical probing instruments; how probers can fit into an overall debug scheme. The course will include in-depth discussion of probing technologies and provide hands-on experience with several types of probing equipment and state-of-the-art design debug tools, including time-resolved emission, thermally-induced voltage alteration (TIVA), light assisted device alteration (LADA), and soft defect localization (SDL). It also contains "hands on" laboratory experiments involving several of the most popular systems used for design debug.

This course is intended for designers, test engineers, failure analysts, and managers involved in the design debug process.

The course is designed primarily for process engineers and process technicians. The emphasis is on understanding how each individual process step works, and understanding the key process control variables for each step. The functional design of the process tools is also discussed, as are process characterization, monitoring, and control.

Engineers new to semiconductor manufacturing will gain a solid, broad understanding of the entire wafer fab process. Engineers experienced in one or more functional areas of wafer fab will benefit from a thorough understanding of processes in other areas, as well as a better appreciation of process interactions.

Each student will also receive a copy of Microchip Manufacturing by Stan Wolf. This unique, full color book is a "must have" reference text for anyone working in the semiconductor industry.

Semitracks, along with Test and Measurement World, have put together a 4-day course on Failure and Yield Analysis. Failure and Yield Analysis is an increasingly difficult and complex process; engineers are required to locate defects on complex integrated circuits. In many ways, this is akin to locating a needle in a haystack, where the needles get smaller and the haystack gets bigger every year. Engineers are required to understand a variety of disciplines in order to effectively perform failure analysis. This requires knowledge of subjects like: design, testing, technology, processing, materials science, chemistry, and even optics! Failed devices and low yields can lead to customer returns and idle manufacturing lines that can cost a company millions of dollars a day. Your industry needs competent analysts to help solve these problems. This is a multi-day course that offers detailed instruction on a variety of effective tools, as well as the overall process flow for locating and characterizing the defect responsible for the failure.

Semiconductor reliability is at a crossroads. In the past, reliability meant discovering, characterizing and modeling failure mechanisms and determining their impact on the reliability of the circuit. Today, reliability can involve tradeoffs between performance and reliability, assessing the impact of new materials, dealing with limited margins, etc. Analysis and experimentation is now performed at the wafer level instead of the packaging level. This requires knowledge of subjects like: design of experiments, testing, technology, processing, materials science, chemistry, and customer expectations. While reliability levels are at an all-time high level in the industry, rapid changes may quickly cause reliability to deteriorate. Your industry needs competent engineers and scientists to help solve these problems.

Semitracks, Inc. and Semiconductor International have put together a course which will provide an overview of the current business climate, anticipated trends and the associated impact on assembly/packaging roadmaps. There will be an in depth discussion of both high-end CPU roadmaps plus the roadmaps to address the multitude of communications and network devices that are driving the digital revolution.

Semitracks, Inc. and Semiconductor International have assembled a course on IC Packaging Design and Modeling. This course provides an overview of the packaging design process. The course covers current packaging technologies, including chip scale packaging, Ball Grid Array technology and other current concepts. This class focuses on techniques and the importance of thermal and mechanical simulations. Discussions and examples will concentrate on thermal performance simulations, assembly & packaging stresses, package reliability (including solder joint fatigue simulation), and interactions between chip and package. In addition, a special section will be examples of successful wafer level simulations.

Semitracks and Test and Measurement World bring you yet another opportunity to learn from the experts - an intensive 2-day course on ESD and Latchup Design and Technology. Dr. Steven Voldman will cover the design, layout, and technology elements required to minimize the effects of electrostatic discharge and CMOS latchup with today's advanced semiconductor devices. Dr. Voldman will address a variety of technologies including CMOS, BiCMOS and compound semiconductors. The course will be held at the Embassy Suites in Tempe, Arizona from Wednesday, January 18 through Thursday January 19. The course will run from 8 AM to 5 PM with an hour lunch break each day. As a special incentive, attendees can purchase copies of Dr. Voldman's books, ESD: Physics and Devices, and ESD: Devices and Circuits, at a special discounted rate.

To register for our courses, register online or download the registration form. Fax completed registration form to us at 1-866-205-0713, or call us at 1-505-858-0454 to register by phone.

Feedback

If you have a suggestion or a comment regarding our courses, online training, discussion forums, reference materials, or if you wish to suggest a new course or location, please feel free to call us at 1-505-858-0454, or e-mail us at info@semitracks.com.

Home > Newsletters > 2007 February Newsletter

Contact us by Phone at 1-505-858-0454or by E-Mail at info@semitracks.com